Probe tips for airborne instruments used to measure cloud microphysical parameters

ABSTRACT

An instrument for obtaining airborne measurements of cloud microphysical parameters. The instrument comprises supporting arms mounted thereon, optics and a detector for measuring the cloud microphysical parameters The supporting arms define an optical path of the instrument and comprise probe tips affixed thereto. The probe tips comprise an outer portion and an inner portion opposite the outer portion. The inner portion of the tips may comprise an angled section having at least one angled surface shaped to deflect particles away from the optical path of the instrument.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority fromco-pending U.S. application Ser. No. 12/415,314 filed Mar. 31, 2009, andentitled PROBE TIPS FOR AIRBORNE INSTRUMENTS USED TO MEASURE CLOUDMICROPHYSICAL PARAMETERS.

FIELD OF THE TECHNOLOGY

The present invention relates to airborne instrumentation used formeasuring cloud microphysical parameters. In particular, the presentinvention relates to probe tips for use with airborne instruments.

BACKGROUND

The existence of small ice particles has remained a highly debatableissue in the cloud physics community. The first measurements of icecloud particle sizes were obtained in the 1930's with the help ofairborne impactors, yet almost eighty years later, researchers have yetto establish a consensus on whether observations of small ice particleswith diameters <100 μm represent naturally occurring ice particles, orare the result of shattering of larger ice particles with the measuringprobe's arms.

The presence of small ice particles may play a crucial role in theconversion of water vapor into precipitation. Furthermore, this maysignificantly affect radiation transfer in clouds and eventually affectthe radiation budget of the Earth. Currently, small ice particles areincluded in many weather prediction and climate models, despite the factthat their natural occurrence has not yet been fully demonstrated.

The majority of airborne probes that are designed to measure cloudparticles sizes use a laser-based measurement method, e.g. asillustrated in FIGS. 1 A and B. The laser is shone between twosupporting arms 1 which point into the air stream. As cloud particleswith diameters from sub-micron to several centimeters cross through thelaser beam 2, the laser light is blocked or scattered (depending on theinstrument) by the cloud particles. Changes to the laser beam can bemeasured by various types of detectors from which the shapes, sizes andconcentrations of the cloud particles can be determined. Existingtechnology uses semi-spherical or rounded arm tips 3 for the particlemeasurement probes. As shown for example in FIG. 1A, the semi-sphericaltips generate large amounts of shattered, splashed and/or bouncedparticle fragments that are deflected into the sample volume of theprobes.

It has been assumed for many years that cloud particles that shattered,splashed or bounced off of the protruding measurement arms, and whichsubsequently passed through the laser beam, would have an insignificanteffect on the measurements of the cloud particle sizes andconcentrations. This assumption is no longer deemed to be correct, andsignificant effort has been made to understand this phenomenon. Dataprocessing methods to correct for the distortions in the natural cloudparticle spectra caused by the particle shattering have been developed(Korolev et al., Journal of Atmospheric and Oceanic Technology, 2005,22:528-542; Lawson et al., Journal of Applied Meteorology andClimatology, 2006, 45:1291-1303) and alternate methods of datacollection using non-airborne instrumentation have also been pursued(Mertes et al., Aerosol Science and Technology, 2007, 41:848-864).

Despite these efforts, there continues to be a need for improved icecloud particle measuring instrumentation that reduces the cloud particleshattering effect previously seen in cloud particle spectra.

SUMMARY

It is therefore an object of the invention to provide improved airborneinstrumentation used for measuring cloud microphysical parameters.

The invention relates to modified probe tips having an asymmetric shapeto minimize both the surface area and length of edges which, uponimpact, deflect particles towards the sample volume of the probe. Theouter part of the tips consists of a pyramidal section having eitherflat or concave surfaces in order to minimize water shedding from theouter part of the tip towards the inner part and to prevent water fromgetting into the optical widows.

The invention further relates to an area of the probe arm in front ofthe optical window having a trap for water shedding along the armsurface, to prevent this water from entering the optical window. Thewater trap may comprise a narrow groove that expands towards its edges.The purpose of this expansion is to generate the air suction inside thegroove to channel the shedding water away from the optical window.

There is accordingly provided herein an instrument for obtainingairborne measurements of cloud microphysical parameters. The instrumentcomprises supporting arms mounted thereon, optics and a detector formeasuring the cloud microphysical parameters. The supporting arms definean optical path of the instrument. The instrument further comprises tipsaffixed to the supporting arms having an outer portion for deflectingparticles away from the optical path of the instrument and an innerportion opposite the outer portion, The outer portion of the tipscomprise a pyramidal section having a centre ridgeline and flat orconcave surfaces effective to reduce water shedding from the outerportion of the tip towards the inner portion.

Also provided herein is a probe tip for airborne instruments used tomeasure cloud microphysical parameters. The probe tip has an outerportion for deflecting particles away from an optical path of theinstrument, and an inner portion opposite the outer portion. The outerportion of the tip comprises a pyramidal section having a centreridgeline and flat or concave surfaces effective to reduce watershedding from the outer portion of the tip towards the inner portion.

There is also provided a method of reducing particle shattering duringcollection of airborne measurements of cloud microphysical parameters.The method comprises steps of:

-   -   providing an airborne cloud particle measuring instrument with        supporting arms mounted onto the instrument, optics and a        detector for measuring the cloud microphysical parameters, the        supporting arms defining an optical path of the instrument;    -   providing tips for the supporting arms having an outer portion        for deflecting particles away from the optical path of the        instrument and an inner portion opposite the outer portion, the        outer portion of the tips comprising a pyramidal section having        a centre ridgeline and flat or concave surfaces effective to        reduce water shedding from the outer portion of the tip towards        the inner portion; and    -   collecting measurements in flight of cloud microphysical        parameters using said airborne cloud particle measuring        instrument, wherein the particle shattering observed in the        collected measurements is reduced.

In certain embodiments, the centre ridgeline may have a concavecurvature, or it may be straight. Similarly, the outer surfaces of thepyramidal section may be flat or concave.

There is also provided herein an instrument for obtaining airbornemeasurements of cloud microphysical parameters comprising supportingarms mounted on the instrument and housing optics and a detector formeasuring said cloud microphysical parameters, the supporting armsdefining an optical path of the instrument; and tips affixed to thesupporting arms comprising an outer portion and an inner portionopposite the outer portion, the inner portion of the tips comprising anangled section having at least one angled surface shaped to deflectparticles away from the optical path of the instrument.

Additionally, there is provided a probe tip for airborne instrumentsused to measure cloud microphysical parameters, the probe tip having anouter portion and an inner portion opposite the outer portion, the innerportion of the tip comprising an angled section having at least oneangled surface shaped to deflect particles away from an optical path ofthe instrument.

The probe tips described above, in certain preferred embodiments, canreduce particle bouncing from the inner portion/surface of the tips whenused at a non-zero angle of attack, as compared to tips which have aconventional inner portion/surface configuration.

Further provided is a method of reducing particle shattering duringcollection of airborne measurements of cloud microphysical parameters,the method comprising:

-   -   providing an airborne cloud particle measuring instrument        comprising supporting arms mounted onto the instrument and        housing optics and a detector for measuring said cloud        microphysical parameters, the supporting arms defining an        optical path of the instrument;    -   providing tips for the supporting arms comprising an outer        portion and an inner portion opposite the outer portion, the        inner portion of the tips comprising an angled section having at        least one angled surface shaped to deflect particles away from        an optical path of the instrument; and    -   collecting measurements in flight of cloud microphysical        parameters using the airborne cloud particle measuring        instrument, wherein the particle shattering observed in the        collected measurements is reduced.

In certain non-limiting embodiments of the above instruments andmethods, the angled section of the inner portion of the tips maycomprise two angled surfaces coming together and forming an edge. Infurther embodiments, the edge formed by the two angled surfaces maycouch the optical window. In addition, the edge may be about parallel toairflow.

In other embodiments, which are also non-limiting, the angled section ofthe inner portion of the tips may comprise two front angled surfacesdefining a first edge and two rear angled surfaces defining a secondedge, the edge formed by the two front angled surfaces being slantedtoward the outer portion of the tips. In further embodiments, the secondedge formed by the two rear angled surfaces may couch the opticalwindow. In addition, the second edge may be about parallel to airflow,and the first edge may form a non-zero angle with respect to theairflow. In addition, the two front angled surfaces of the tip may, incertain non-limiting embodiments, form an angle such that particles,after impact, are bounced away from the sample volume of the probe.

In further embodiments of the above instruments and methods, the opticsare laser-based optics. As an example, the instrument may be an OAP-2DC,OAP-2DP, HVPS, CIP, FSSP, CPI, CAPS and SID-type airborne cloud particleinstrument.

In still further embodiments, the supporting arms or the tips affixedthereto each comprise an optical window through which light from theoptics of the instrument passes along said optical path. The supportingarms or tips may optionally include a water trap to prevent water shedalong the arm surface from entering the optical window. In suchembodiments, the water trap may preferably form a narrow groove forwardof the optical window that expands towards its edges to channel theshedding water away from the optical window.

Also provided herein is an instrument for obtaining airbornemeasurements of cloud microphysical parameters comprising: supportingarms mounted on the instrument and housing optics and a detector formeasuring said cloud microphysical parameters, the supporting armsdefining an optical path of the instrument; and tips affixed to thesupporting arms; wherein the supporting arms or the tips respectivelyaffixed thereto each comprise an optical window through which light fromthe optics of the instrument passes along said optical path, and whereinthe supporting arms or the tips respectively affixed thereto furthercomprise a water trap to prevent water shed along the tip and/or armsurface from entering the optical window.

A probe tip is further provided for airborne instruments used to measurecloud microphysical parameters, the probe tip comprising a water trap toprevent water shed along the tip surface from entering an optical windowthrough which light from optics of the instrument passes.

The modified arm tips and water trap for the airborne cloud particlemeasurement probes mitigate the effect of ice particle shattering anddroplet splashing on the measurements of cloud particle sizes, shapesand concentrations.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent fromthe following description in which reference is made to the appendeddrawings wherein:

FIG. 1 is a conceptual diagram of the mechanism of particle shatteringduring sampling by (A) OAP-2DC, OAP-2DP, HVPS, and CIP-type airbornecloud particle instruments, and (B) FSSP, CPI, CAPS and SID-typeairborne cloud particle instruments, due to the mechanical impact withprobe parts upstream of the sample area;

FIG. 2 is a photographical representation of ice particle shatteringcaused by mechanical impact with probe parts upstream of the sample areain a OAP-2DC arm during wind tunnel testing (Cox Wind Tunnel, D˜2.5 cm,TAS˜70 m/s);

FIG. 3 is a photographical representation of conical FSSP arm tips, theFSSP probe installed inside a wind tunnel compartment;

FIG. 4 is a photographical representation of the conical FSSP arm tipsshown in FIG. 3 during exposure to high speed supercooled liquid spray,and illustrating the ice build-up on the tip surface exposed to theairflow;

FIG. 5 is a close-up view of the conical FSSP arm tips shown in FIG. 4,showing (A) the streaks of frozen water shed along the inner tip'ssurface formed when the tip heaters were turned off; and (B) refrozenwater on the unheated section of the arm tip in the form of an iceridge, resulting from the water shed along the inner tip surface;

FIG. 6 is a photographical representation of conical OAP-2DC arm tipsbased on the design published in Korolev et al., J. Atm. Ocean. Techn(2005; supra) during wind tunnel testing (Cox Wind Tunnel, D˜2.5 cm,TAS˜70 m/s), and showing refrozen water on the unheated section of thearm. The build up of the refrozen water around the whole arm suggeststhat the water sheds along both inner and outer surface of the arm, andwhen water sheds along the inner part of the arm surface it may get intothe optical window;

FIG. 7 is a photographical representation of conical FSSP arm tips basedon the design published in Korolev et al., J. Atm. Ocean. Techn (2005;supra) installed inside a wind tunnel compartment during wind tunneltesting (Cox Wind Tunnel, D˜2.5 cm, TAS˜70 m/s) and showing build up ofrefrozen water around the whole unheated section of the arm, suggestingthat the water sheds along both inner and outer surfaces of the arm andthat water shed along the inner part of the arm surface may get into theoptical window;

FIG. 8 shows (A) modified pyramidal OAP-2DC arm tips according to anexample of one embodiment of the invention, and (B) the arm tips of (A)mounted onto the forward portion of an OAP-2DC measuring probe; theouter part of the tips consisting of either flat or concave surfaces inorder to minimize water shedding from the outer part of the tip towardsthe inner part and to prevent water from getting into the opticalwindows;

FIG. 9 shows modified pyramidal arm tips according to further examplesof an embodiment of the invention, having a curved pyramidal outer tipportion with concave ridgeline (A), a curved pyramidal outer tip portionwith straight ridgeline (B), and a flat pyramidal outer tip portion withstraight ridgeline (C);

FIG. 10A is an expanded view of the bottom pyramidal OAP-2DC arm tipshown in FIG. 8A; illustrating the optical window of the probe and awater trap for directing water shed along the arm surface away from theoptical window;

FIG. 10B is an expanded view of a possible alternate embodiment of thepyramidal OAP-2DC arm tip shown in FIG. 8A;

FIG. 11 illustrates the results of the flow analysis for tips with awater trap. The flow analysis was performed for 150 m/s, P=800 mb andT=0C;

FIG. 12 depicts snapshots from high speed video showing the performanceof an embodiment of arm tips incorporating a water trap. Experimentswere performed in the Cox wind tunnel in liquid spray at 80 m/s, 10 degangle of attack. The video was recorded by NASA Glenn video group;

FIG. 13 is a photographical representation of pyramidal OAP-2DC arm tipsaccording to an embodiment of the invention, mounted onto the forwardportion of an OAP-2DC measuring probe installed inside a wind tunnelcompartment during wind tunnel testing (Cox Wind Tunnel, D˜2.5 cm,TAS˜70 m/s) and showing minimal build up of refrozen water around theinner part of the arm surface, suggesting significant reduction in theamount of water shed along the inner arm surface and therefore reducedamounts of water getting into the optical window;

FIGS. 14A and B illustrate modified OAP-2DC arms of additional exemplaryembodiments of the invention, each having different arm configurations;

FIGS. 15A and B illustrate modified OAP-2DC arms of further exemplaryembodiments of the invention, each having different arm configurations;

FIGS. 16A-D illustrate modified Cloud Particle Imager (CIP) tip arms ofyet further exemplary embodiments of the invention, incorporating apyramidal CIP arm tip design;

FIGS. 17A and B illustrate modified OAP-2DC probe tips of furtherexemplary embodiments of the invention, with modifications to the innerportion thereof;

FIG. 18 shows an embodiment of the modified probe tip design shown inFIG. 17B and the trajectory of particles after bouncing from the probetip surface;

FIG. 19 illustrates top (A and B), side (C) and front (D) views ofmodified CIP probe tips of additional exemplary embodiments of theinvention, with modifications to the inner portion thereof;

FIG. 20 illustrates side (A), front (B) and top (C and D) views ofmodified CIP probe tips according to further exemplary embodiments ofthe invention, with modifications to the inner portion thereof;

FIG. 21 show images taken during testing of modified OAP-2DC probe tipsof the design shown in FIG. 17B in the Cox wind tunnel in ice (A) andliquid (B) sprays at 80 m/s;

FIG. 22 show images taken during testing of modified CIP probe tips ofthe design shown in FIG. 20 in ice (A) and liquid (B) sprays at 80 m/s;and

FIG. 23 shows comparative test results of prior art CIP (A), FSSP (B)and OAP-2DC (C) probe tips in the Cox wind tunnel in ice sprays at 80m/s.

DETAILED DESCRIPTION

High speed video recording of bouncing and shattering of ice particlesconducted in wind tunnels has been obtained by NASA in cooperation withEnvironment Canada confirming that ice particles can shatter and bounceinto the sample volume of the particle probes. This is clearly evidentin the photograph shown in FIG. 2, where ice particles 4 can be seenbouncing off the semi-spherical probe tip 3 of the probe arm 1 duringwind tunnel testing.

Until now, it has been generally believed that the shattered particlescould be identified and eliminated during analysis of the cloud particlespectral data, and thus no attempts have been made to redesign theprobes' arm tips to mitigate shattering.

The present inventor has modified the probe tips with a view tominimizing the effect of cloud particle shattering. This approach isparticularly desirable over the data correction methods currently inuse, for instance, since (i) ice particle shattering with standardOAP-2DC arms is thought to result in the overestimation of the measuredconcentration ten fold or more; and (ii) for some instruments (e.g.OAP-2DC) existing algorithms are incapable of filtering out allshattering events.

The well-known semi-spherical probe tips were replaced with (i) conicaland (ii) pyramidal probe tips and tested in wind tunnel experiments toascertain which design has the greatest effect in reducing the effect ofice shattering on measurements.

The configuration of the wind tunnel testing compartment can be seen inFIG. 3, in which a FSSP probe is installed having conical tips 3 on theprobe arms 1. When exposed to high-speed supercooled liquid spray withinthe test environment, ice build-up 5 can be seen on the tip surfaceexposed to the airflow (FIG. 4). However, as is better seen in theclose-up view of the conical FSSP arm tips in FIG. 5, when the tipheaters are turned off streaks of frozen water A can be observed. Theseare shed along the inner tip's surface and cause a build up of refrozenwater on the unheated section of the arm tip in the form of an ice ridgeB. The water shed along the inner tip surface may also enter the opticalwindow 10 of the probe arm.

Wind tunnel testing was also undertaken using an OAP-2DC probe fittedwith conical arm tips. This conical OAP-2DC arm tip design is based onthe design published in Korolev et al., J. Atm. Ocean. Techn (2005;supra). As is observed in FIG. 6 and similar to the results obtainedusing conical FSSP probe tips, refrozen water builds up on the unheatedsections of the OAP-2DC arms during wind tunnel tests (Cox Wind Tunnel,D˜2.5 cm, TAS˜70 m/s). The build up of the refrozen water 6 around thewhole arm suggests that the water sheds along both inner and outersurfaces of the arm. Thus, when water sheds along the inner part of thearm surface it may enter the optical window 10 and interfere with theoptical measurements of the probe.

For comparative purposes, conical FSSP arm tips based on the designpublished in Korolev et al., J. Atm. Ocean. Techn (2005; supra) werealso tested as described above for the OAP-2DC probe (Cox Wind Tunnel,D˜2.5 cm, TAS˜70 m/s). Results of the wind tunnel experiments, portrayedin the photograph of FIG. 7, showed refrozen water 6 built up around thewhole unheated section of the arm, similarly suggesting that the watersheds along both inner and outer surfaces of the arm and that the watershed along the inner part of the arm surface may get into the opticalwindow 10.

FIG. 8A shows modified pyramidal OAP-2DC arm tips according to anexample of one embodiment of the invention. According to the exampleshown, the tips have an outer pyramidal tip portion 12 designed todeflect water, ice or other cloud particles away from the inner surfaceof the probe tip. The pyramidal tip portion 12 has a center ridgeline 13and outer surfaces 15 a and 15 b. The pyramidal tips can be installed onthe arms 1 of an OAP-2DC probe, which are in turn mounted onto theforward portion 11 of the instrument as illustrated in FIG. 8B accordingto means commonly known in the art, for instance via mounting flanges 9.

In further exemplary embodiments, as illustrated in FIGS. 9A-B, theouter surfaces 15 a and 15 b of the probe tips may be concave.Alternatively, the outer surfaces 15 a and 15 b of the probe tips may beflat as can be seen in FIG. 9C. In addition, the center ridgeline 13 ofthe probe tips may be concave as illustrated in FIG. 9A, or straight asillustrated in FIGS. 9B and C. In certain embodiments it may bedesirable to incorporate concavity into outer surfaces 15 a and 15 band/or curvature into the center ridgeline 13 of the outer pyramidalportion 12, to further mitigate the shedding from the outer part of thetip towards the inner part and reduce the shattering effect caused bysmall water, ice or other cloud particles during operation. However, inother embodiments a straight center ridgeline 13 and flat outer surfaces15 a and 15 b of the probe tips may be sufficient for reducing theshattering effect.

FIG. 10A depicts the bottom pyramidal OAP-2DC arm tip shown in FIG. 8Ain expanded view, in order to better illustrate the optical window 10 ofthe probe and an optional water trap 17. The water trap 17 may comprisea notch, trough, groove or other formation in the upper surface of theprobe arm 1 effective to direct water which is shed along the inner armsurface away from the optical window 10. The water trap 17 may bemachined or otherwise formed to the desired depth and dimensions basedon the type of cloud particle instrumentation. As depicted, the watertrap 17 is machined into the probe arm immediately forward of theoptical window. A possible alternate embodiment of the water trap 17 canalso be seen in FIG. 10B.

Results of flow analysis for tips with the groove can be seen in FIG.11. The flow analysis shows that the air moving along the surface of thetip gets inside the water trap at position 1 and exits out through thesides of the water trap. The flow analysis was performed for 150 m/s,P=800 mb and T=0C.

FIG. 12 shows snapshots from high speed video showing the performance oftips with the water trap in the Cox wind tunnel in liquid spray at 80m/s, 10 deg angle of attack. The video was recorded by NASA Glenn videogroup. Both images 12A and 12B show water droplets shedding over thesurface of the tip at position 1, and dumped water released from thewater trap at position 2.

Pyramidal arm tips as described above and illustrated in FIGS. 8-10 weremounted onto the forward portion of an OAP-2DC measuring probe installedinside a wind tunnel compartment and tested according to similar windtunnel testing used for the conical arm tips (Cox Wind Tunnel, D˜2.5 cm,TAS˜70 m/s). The results of this testing are depicted in FIG. 13, andshow that minimal amounts of refrozen water build up around the innerparts of the arm surfaces, suggesting a significant reduction in theamount of water shed along the inner arm surface and therefore reducedamounts of water getting into the optical window. Accordingly, thesetests suggest that the effect on cloud particle size distributionmeasurements by water, ice or other cloud particle shattering on thearms of cloud microphysical instruments can be significantly reducedthrough the use of pyramidal arm tips as described herein. The pyramidalarm tips are a substantial improvement over the semi-spherical arm tipscommonly used in the art, and also represent a marked improvement overthe conical tip option as described herein.

Based on the observations made during testing, pyramidal arm tips asdescribed herein reduce the effect of shattering, splashing and bouncingon the measurements of particle shape, size and concentration.Preliminary estimates suggest that concentrations of cloud particles maybe changed by up to a factor of twenty, depending on the size of thecloud particles. The suggested solution significantly reduces the effectof the shattering, splashing and bouncing on measurements.

Additional embodiments of the pyramidal probe tips of the invention canbe envisioned, for instance as illustrated in FIGS. 14-16. ModifiedOAP-2DC arms having different arm configurations are seen in FIGS. 14Aand B and FIGS. 15A and B, each having pyramidal arm tips with outersurfaces 15 a and 15 b and a center ridgeline 13. Similarly,modifications to Cloud Particle Imager (CIP) tip arms can be envisioned,such as that illustrated in FIGS. 16A-D whereby pyramidal arm tips withouter surfaces 15 a and 15 b and a center ridgeline 13 are incorporatedinto the CIP tip design. Similar modifications may be made toincorporate pyramidal probe tips into other similar airborne cloudparticle instruments, for instance OAP-2DP, HVPS, FSSP, CPI, CAPS andSID-type airborne cloud particle instruments.

FIGS. 17A and 17B show additional modifications of the probe tipsaccording to further embodiments of the invention which mitigate theeffect of shattering on measurements of ice particles. In theillustration of FIG. 17A, which is non-limiting embodiment showing themodifications on an OAP-2DP probe tip, the inner surface of the probetips consists of two surfaces 20 a,b coming together and forming an edge25, which couches the optical window 10 for the laser beam. The edge 25is designed to be parallel to the airflow. In the illustration of FIG.17B, which is also a non-limiting embodiment, the inner surface of theprobe tips consists of four surfaces created in such a way that thefirst or front edge 35 between the two front surfaces 30 a,b is slantedtoward the outer side forming a non-zero angle with the airflow. Thesecond two surfaces 32 a,b form a second or rear edge 37 parallel to theairflow. The optical window 10 is located downstream from theintersection 40 of the two edges 35 and 37. The two front surfaces 30a,b of the probe tip in FIG. 17B form an angle such that particles,after impact, are bounced away from the sample volume of the probe. Thetrajectory of the particles, after bouncing from the surface of theprobe tips, is shown in FIG. 18 (the resistance of the air isneglected).

The modified probe tips illustrated in FIGS. 17A and B work well at azero angle of attack (AoA) although they are particularly advantageousat a non-zero angle of attack. Without such modifications, particles(e.g. ice, liquid droplets) may bounce from the inner surface of the tipand be directed toward the sample volume of the instrument, which canaffect accuracy of the measurements. The modified probe tips illustratedin FIGS. 17A and 17B are designed to be insensitive to the angle ofattack.

The probe tips illustrated in FIG. 17B have the added advantage that ata non-zero angle of attack the upstream section of the tip is notprojected to the sample volume, and thus it does not block the particlesfrom freely passing through the sampling volume. In other words, thesample area stays the same for the angle of attack varying in the range−α<AoA<α, where α is the angle between the first or front edge 35 andthe axis of the arm 1. For the probe tips in FIG. 17A the sample areashould be corrected for the angle of attack due to the blockage of theparticles.

FIGS. 19A-D and 20A-D show further non-limiting embodiments of CIP probetips incorporating similar modifications to those illustrated in FIGS.17A and B. In FIG. 19, several views (A to D) are provided to illustrateangled inner surfaces of the CIP probe tips. Similar to the OAP-2D tipsrepresented in FIG. 17A, the inner surface of the CIP probe tipsconsists of two surfaces 50 a,b coming together and forming an edge 45,which couches the optical window 10 for the laser beam. The edge 45 isdesigned to be parallel to the airflow.

In FIG. 20, views A to D illustrate the angled inner surfaces of asecond non-limiting embodiment the CIP probe tips. Similar to the OAP-2Dtip represented in FIG. 17B, the inner surface of the probe tipsconsists of four surfaces. The first or front edge 55 between the twofront surfaces 60 a,b is slanted toward the outer side or portion of thetip forming a non-zero angle with the airflow. The second two surfaces62 a,b form a second or rear edge 57 parallel to the airflow. Theoptical window 10 is located downstream from the intersection 70 of thetwo edges 55 and 57. The two front surfaces 60 a,b of the probe tip forman angle such that particles, after impact, are bounced away from thesample volume of the probe.

High speed videos were taken during testing of the modified tips in theCox wind tunnel in order to demonstrate their performance in ice andliquid sprays at 80 m/s. FIGS. 21 and 22 show images taken during thesetests for the OAP-2DC design (ice FIG. 21A; liquid spray FIG. 21B) andfor the CIP probe tip design (ice FIG. 22A; liquid spray FIG. 22B). Iceand liquid particles appear in these images as bright lines. As seenfrom these images all ice and liquid particle tracks are horizontallines, which indicates that those particles are following the airstream.No examples of the particle bouncing towards the sample area were found,which would result in particle tracks crossing the airstreams. This is asignificant improvement over previous tip designs, as demonstrated bycomparative tests with prior art models of CIP (FIG. 23A), FSSP (FIG.23B) and OAP-2DC (FIG. 23C) probe tips. As can be seen from thenon-horizontal particle tracks in these images, substantial evidenceexists for particles bouncing towards the sample volume using theseprior art designs.

One or more currently preferred embodiments have been described by wayof example. It will be apparent to persons skilled in the art that anumber of variations and modifications can be made without departingfrom the scope of the invention as defined in the claims.

1. An instrument for obtaining airborne measurements of cloudmicrophysical parameters, said instrument comprising: supporting armsmounted on the instrument and housing optics and a detector formeasuring said cloud microphysical parameters, the supporting armsdefining an optical path of the instrument; and tips affixed to thesupporting arms comprising an outer portion and an inner portionopposite the outer portion, the inner portion of the tips comprising anangled section having at least one angled surface shaped to deflectparticles away from the optical path of the instrument.
 2. Theinstrument according to claim 1, wherein the optics are laser-basedoptics.
 3. The instrument according to claim 1, wherein the instrumentis an airborne cloud particle instrument selected from OAP-2DC, OAP-2DP,HVPS, CIP, FSSP, CPI, CAPS and SID-type instruments.
 4. The instrumentaccording to claim 1, wherein the supporting arms or the tipsrespectively attached thereto each comprise an optical window throughwhich light from the optics of the instrument passes along said opticalpath.
 5. The instrument according to claim 4, wherein the supportingarms or the tips respectively attached thereto further comprise a watertrap to prevent water shed along the tip and/or arm surface fromentering the optical window.
 6. The instrument according to claim 5,wherein the water trap comprises a narrow groove forward of the opticalwindow that expands towards its edges to channel the shedding water awayfrom the optical window.
 7. The instrument according to claim 1, whereinthe angled section of the inner portion of the tips comprises two angledsurfaces coming together and forming an edge.
 8. The instrumentaccording to claim 4, wherein the angled section of the inner portion ofthe tips comprises two angled surfaces coming together and forming anedge which couches the optical window.
 9. The instrument according toclaim 7, wherein the edge is about parallel to airflow.
 10. Theinstrument according to claim 8, wherein the edge is about parallel toairflow.
 11. The instrument according to claim 1, wherein the angledsection of the inner portion of the tips comprises two front angledsurfaces defining a first edge and two rear angled surfaces defining asecond edge, the edge formed by the two front angled surfaces is slantedtoward the outer portion of the tips.
 12. The instrument according toclaim 4, wherein the angled section of the inner portion of the tipscomprises two front angled surfaces defining a first edge and two rearangled surfaces defining a second edge, the first edge formed by the twofront angled surfaces is slanted toward the outer portion of the tips,and the second edge couches the optical window downstream from theintersection of the first and second edges.
 13. The instrument accordingto claim 11, wherein the second edge is about parallel to airflow. 14.The instrument according to claim 12, wherein the second edge is aboutparallel to airflow.
 15. The instrument according to claim 11, whereinthe first edge forms a non-zero angle with respect to the airflow. 16.The instrument according to claim 12, wherein the first edge forms anon-zero angle with respect to the airflow.
 17. The instrument accordingto claim 11, wherein the two front angled surfaces of the tip form anangle such that particles, after impact, are bounced away from thesample volume of the probe.
 18. The instrument according to claim 12,wherein the two front angled surfaces of the tip form an angle such thatparticles, after impact, are bounced away from the sample volume of theprobe.
 19. The instrument according to claim 1, wherein the outerportion of the tips consists of a pyramidal section having either flator concave surfaces effective to minimize water shedding from the outerportion of the tip towards the inner portion and shaped to deflectparticles away from the optical path of the instrument.
 20. A probe tipfor an airborne instrument used to measure cloud microphysicalparameters, the probe tip having an outer portion and an inner portionopposite the outer portion, the inner portion of the tip comprising anangled section having at least one angled surface shaped to deflectparticles away from an optical path of the instrument.
 21. The probe tipaccording to claim 20, further comprising an optical window throughwhich light from optics of the instrument passes along said opticalpath.
 22. The probe tip according to claim 21, further comprising awater trap to prevent water shed along the tip from entering the opticalwindow.
 23. The probe tip according to claim 22, wherein the water trapcomprises a narrow groove forward of the optical window that expandstowards its edges to channel the shedding water away from the opticalwindow.
 24. The probe tip according to claim 20, wherein the angledsection of the inner portion of the tip comprises two angled surfacescoming together and forming an edge.
 25. The probe tip according toclaim 21, wherein the angled section of the inner portion of the tipcomprises two angled surfaces coming together and forming an edge whichcouches the optical window.
 26. The probe tip according to claim 24,wherein the edge is about parallel to airflow.
 27. The probe tipaccording to claim 25, wherein the edge is about parallel to airflow.28. The probe tip according to claim 20, wherein the angled section ofthe inner portion of the tip comprises two front angled surfacesdefining a first edge and two rear angled surfaces defining a secondedge, the edge formed by the two front angled surfaces is slanted towardthe outer portion of the tip.
 29. The probe tip according to claim 21,wherein the angled section of the inner portion of the tip comprises twofront angled surfaces defining a first edge and two rear angled surfacesdefining a second edge, the first edge formed by the two front angledsurfaces is slanted toward the outer portion of the tip, and the secondedge couches the optical window downstream from the intersection of thefirst and second edges.
 30. The probe tip according to claim 28, whereinthe second edge is about parallel to airflow.
 31. The probe tipaccording to claim 29, wherein the second edge is about parallel toairflow.
 32. The probe tip according to claim 28, wherein the first edgeforms a non-zero angle with respect to the airflow.
 33. The probe tipaccording to claim 29, wherein the first edge forms a non-zero anglewith respect to the airflow.
 34. The probe tip according to claim 28,wherein the two front angled surfaces of the tip form an angle such thatparticles, after impact, are bounced away from the sample volume of theprobe.
 35. The probe tip according to claim 29, wherein the two frontangled surfaces of the tip form an angle such that particles, afterimpact, are bounced away from the sample volume of the probe.
 36. Theprobe tip according to claim 20, wherein the outer portion of the tipconsists of a pyramidal section having either flat or concave surfaceseffective to minimize water shedding from the outer portion of the tiptowards the inner portion and shaped to deflect particles away from theoptical path of the instrument.
 37. The probe tip according to claim 20,adapted for attachment to a supporting arm of an airborne cloud particleinstrument selected from OAP-2DC, OAP-2DP, HVPS, CIP, FSSP, CPI, CAPSand SID-type instruments.
 38. A method of reducing particle shatteringduring collection of airborne measurements of cloud microphysicalparameters, said method comprising: providing an airborne cloud particlemeasuring instrument comprising supporting arms mounted onto theinstrument and housing optics and a detector for measuring said cloudmicrophysical parameters, the supporting arms defining an optical pathof the instrument; providing tips for the supporting arms comprising anouter portion and an inner portion opposite the outer portion, the innerportion of the tips comprising an angled section having at least oneangled surface shaped to deflect particles away from an optical path ofthe instrument; and collecting measurements in flight of cloudmicrophysical parameters using said airborne cloud particle measuringinstrument, wherein the particle shattering observed in the collectedmeasurements is reduced.
 39. The method according to claim 38, whereinthe angled section of the inner portion of the tips comprises two angledsurfaces coming together and forming an edge.
 40. The method accordingto claim 38, wherein the angled section of the inner portion of the tipscomprises two front angled surfaces defining a first edge and two rearangled surfaces defining a second edge, the edge formed by the two frontangled surfaces is slanted toward the outer portion of the tip.
 41. Themethod according to claim 38, wherein the outer portion of the tipsconsists of a pyramidal section having either flat or concave surfaceseffective to minimize water shedding from the outer portion of the tiptowards the inner portion and shaped to deflect particles away from theoptical path of the instrument.
 42. The method according to claim 38,wherein the airborne cloud particle measuring instrument is selectedfrom OAP-2DC, OAP-2DP, HVPS, CIP, FSSP, CPI, CAPS and SID-typeinstruments.
 43. The method according to claim 38, wherein thesupporting arms or tips each comprise an optical window through whichlight from the optics of the instrument passes along said optical path,and a water trap to prevent water shed along the arm or tip surface fromentering the optical window.
 44. An instrument for obtaining airbornemeasurements of cloud microphysical parameters, said instrumentcomprising: supporting arms mounted on the instrument and housing opticsand a detector for measuring said cloud microphysical parameters, thesupporting arms defining an optical path of the instrument; and tipsaffixed to the supporting arms wherein the supporting arms or the tipsrespectively affixed thereto each comprise an optical window throughwhich light from the optics of the instrument passes along said opticalpath, and wherein the supporting arms or the tips respectively affixedthereto further comprise a water trap to prevent water shed along thetip and/or arm surface from entering the optical window.
 45. Theinstrument according to claim 44, wherein the water trap comprises anarrow groove forward of the optical window that expands towards itsedges to channel the shedding water away from the optical window. 46.The instrument according to claim 44, wherein the instrument is anairborne cloud particle instrument selected from OAP-2DC, OAP-2DP, HVPS,CIP, FSSP, CPI, CAPS and SID-type instruments.
 47. A probe tip for anairborne instrument used to measure cloud microphysical parameters, theprobe tip comprising a water trap to prevent water shed along the tipsurface from entering an optical window through which light from opticsof the instrument passes.
 48. The probe tip of claim 47, furthercomprising said optical window.
 49. The probe tip according to claim 46,wherein the water trap comprises a narrow groove forward of the opticalwindow that expands towards its edges to channel the shedding water awayfrom the optical window.
 50. The probe tip according to claim 47,wherein the probe tip is for an airborne cloud particle instrumentselected from OAP-2DC, OAP-2DP, HVPS, CIP, FSSP, CPI, CAPS and SID-typeinstruments.